1. Field of the Invention
The invention relates generally to methods for making carbon nanotubes and, particularly, to a method for making the branched carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNTs) were first discovered by S. Iijima (Nature, vol. 354, pp. 56-58, 1991) and were synthesized by T. W. Ebbesen and P. M. Ajayan (Nature, vol. 358, pp. 220-222, 1992). Theoretical studies show that carbon nanotubes exhibit either metallic or semiconductive behavior depending on the radii and helicity of the nanotubes. CNTs have interesting and potentially useful electrical and mechanical properties and offer potential for use in electronic devices such as field emission displays, micro electron sources in vacuum, and nano-scale devices. Particularly, the branched CNTs have the unique electrical and thermal properties due to a three-terminal/three-dimensional tubular structure. Therefore, the branched CNTs can be widely used in the nano-scale integrated circuits.
At present, the traditional methods for making the branched CNTs include an arc-discharge method, a template method, and a metal organic chemical vapor deposition (MOCVD) method. The arc-discharge method has low yield, the template method has a complex process, and the prevalent method is the MOCVD method. The MOCVD method is costly in manufacture due to use of a metal organic gas as a raw material and cannot form the branched CNTs in a predetermined area. Thus, the application of the MOCVD method in the nano-scale integrated circuits is limited.
What is desired is a low-cost, high-yield, and simple method for making the branched CNTs in a predetermined/chosen area/location.